"The changes I have outlined tonight are aimed at ensuring the survival of a young democracy that is fighting for its life in a part of the world of enormous importance to American security," Bush said in a nationally televised address. "The question is whether our new strategy will bring us closer to success. I believe that it will."

Bush's optimism was immediately challenged by Democratic leaders, who repeated their opposition to increasing troop levels. Even some Republicans criticized the plan.

The president acknowledged previous failures.

"Where mistakes have been made, the responsibility rests with me," he said. Past efforts to quell violence in Baghdad failed, he said, because "there were not enough Iraqi and American troops to secure neighborhoods" and "there were too many restrictions on the troops we did have."

He said his plan would remedy such flaws.

In earlier operations, the president said, "political and sectarian interference prevented Iraqi and American forces from going into neighborhoods that are home to those fueling the sectarian violence."

"This time, Iraqi and American forces will have a green light to enter those neighborhoods," Bush said.